Hand Crank Low Battery Recovery: Difference between revisions
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The problem is that while the power provided by the yo-yo will eventually trickle charge the battery, it is very inefficient. We need to develop a way to dump more of the power from the hand generator into the battery. |
The problem is that while the power provided by the yo-yo will eventually trickle charge the battery, it is very inefficient. We need to develop a way to dump more of the power from the hand generator into the battery. |
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==Solutions== |
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One thought is to redesign the 3VPCU rail to be more independent of VIN. |
One thought is to redesign the 3VPCU rail to be more independent of VIN. |
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Revision as of 06:21, 13 March 2007
This page describes the problems with recovering from an extremely discharged battery when using a human powered generator.
These problems were first discussed in the March 9-10 XO design review meeting in Cambridge.
Problem Description
The problem only occurs in the case of trying to recharge a battery which has been extremely discharged using only a human powered generator.
Nature of Power Generated by Human Powered Generators
The power generated from a human powered generator such as the yo-yo design currently being considered is periodic in nature. A high voltage (+20V) at reasonable currents is provided when the generator is pulled and for several seconds afterwards. There is usually a similar amount of time between pulls during which no power is supplied.
If a battery is in good condition (not extremely discharged), there should be no problem recharging the battery with power from a human powered generator.
Recovery from a Low Battery Condition
If a laptop attempts to charge an extremely discharged battery (here defined as a battery whose output voltage is less than or equal to 4.8V), it will pull the VIN power rail down to a voltage below that necessary for operation of the laptop. As this causes erratic laptop operation, the embedded controller (EC) is programmed to instead trickle charge batteries which are extremely discharged (including those discharged so low that the chip inside the battery pack is no longer powered).
This trickle charging consists of providing a small current to the battery for a several hundred milliseconds, every couple of seconds. The EC does this continuously whenever it has a valid mains input (ACIN on GPIAD2) and it cannot communicate with the battery pack.
Interaction
The problem is that while the power provided by the yo-yo will eventually trickle charge the battery, it is very inefficient. We need to develop a way to dump more of the power from the hand generator into the battery.
Solutions
One thought is to redesign the 3VPCU rail to be more independent of VIN.
Is it possible for the EC to detect this condition ?